Gas Diffusion, Energy Transport, and Thermal Accommodation in Single‐Walled Carbon Nanotube Aerogels

Abstract

The thermal conductivity of gas-permeated single-walled carbon nanotube (SWCNT) aerogel (8 kg m − 3 density, 0.0061 volume fraction) is measured experimentally and modeled using mesoscale and atomistic simulations. Despite the high thermal conductivity of isolated SWCNTs, the thermal conductivity of the evacuated aerogel is 0.025 ± 0.010 W m − 1 K − 1 at a temperature of 300 K. This very low value is a result of the high porosity and the low interface thermal conductance at the tube-tube junctions (estimated as 12 pW K − 1 ). Thermal conductivity measurements and analysis of the gas-permeated aerogel (H 2 , He, Ne, N 2 , and Ar) show that gas molecules transport energy over length scales hundreds of times larger than the diameters of the pores in the aerogel. It is hypothesized that ineffi cient energy exchange between gas molecules and SWCNTs gives the permeating molecules a memory of their prior collisions. Low gas-SWCNT accommodation coeffi cients predicted by molecular dynamics simulations support this hypothesis. Amplifi ed energy transport length scales resulting from low gas accommodation are a general feature of CNT-based nanoporous materials.

Predicting alloy vibrational mode properties using lattice dynamics calculations, molecular dynamics simulations, and the virtual crystal approximation

“…[1][2][3][4][5][6][7][8][9][10] Disordered lattices are a subgroup of disordered materials where the atomic positions follow a lattice structure but the constituent species are spatially random. Examples include isotopic solids, where the species have the same electronic structure but small mass variations, 11,12 and alloys, our focus here, where at least two distinct species are present.…”

Thermal conductance of the junction between single-walled carbon nanotubes

“…Our focus here is related to single-walled CNT aerogels, which are a high-porosity material (densities q of 6-20 kg/m 3 ) where the individual CNTs form a random network held together by van der Waals interactions. 2,3 For a CNT aerogel in vacuum at a temperature of 300 K, Schiffres et al report a thermal conductivity of 0.025 W/mÁK (q ¼ 8 kg/m 3 , which corresponds to a volume fraction of 0.006), 4 while Zhang et al report a value of 0.055 W/mÁK (q ¼ 6.6 kg/m 3 ). 5 These values are much lower than the 12 W/mÁK predicted from an effective medium approximation for a random network of cylinders using a single-walled CNT thermal conductivity of 3000 W/mÁK.…”

“…5 These values are much lower than the 12 W/mÁK predicted from an effective medium approximation for a random network of cylinders using a single-walled CNT thermal conductivity of 3000 W/mÁK. 4 This result indicates that the thermal conductance of the junctions between CNTs must be taken into account when predicting thermal conductivity.…”

“…Recent measurements on perpendicular junctions between multiwalled CNTs with diameters of 42 to 68 nm, however, indicate that such a scaling is not appropriate as the per unit area conductance shows a diameter dependence. 7 Some estimates of the thermal conductance of the junction between single walled CNTs from thermal conductivity measurements on different network materials suggest values between 2 and 12 pW/K, 4,8,9 while Zhang et al estimate 60 pW/K. 5 Molecular dynamics (MD) simulations 8,10 and atomistic Green's function calculations 8,11 of perpendicular junctions between single-walled CNTs predict thermal conductances between 10 and 100 pW/K at a temperature of 300 K that increase with increasing CNT diameter.…”

A General Perspective of the Characterization and Quantification of Nanoparticles: Imaging, Spectroscopic, and Separation Techniques

“…For instance, it is applied to measure the surface area of FeNPs 221 and the pore size distribution in SWCNTs 231 as well as to conduct toxicity studies.…”